Various endless screw systems are known for forming loops of textile yarn and depositing them on a conveyor belt. One of these systems is illustrated by the British patent application published under No. 2 024 271. A rotating arm coils the yarn around rotatingly driven screws, which results in successively forming loops in the vicinity of the head end of the screw, these loops being displaced axially along the screws due to the rotation of the latter. Given that the yarn loops are directly carried by the screws, friction due to rotation of the latter produces tension in the yarn strands. The yarn loops are moreover deposited on the conveyor belt with the same orientation as that with which they are formed on the screws. To permit easy recovery, that is to say in order not to be obliged to pull the yarn underneath the loops subsequently deposited, whereby the yarn may become entangled which is liable to slow down or even stop the installation, one is generally obliged to carry out a turnover operation which consists in turning the yarn loops around by 180.degree. while they are transported on the conveyor belt, for example, by means of a second, so-called turnover belt.
Known depositing systems generally form substantially round loops which are superposed with a slight axial shift. The formation of round loops presents various drawbacks. One such drawback is that the round loop does not allow a uniform density of the deposited yarn to be achieved, which results in a lack of homogeneous yarn retraction during thermal treatment, in particular of synthetic fibers. The round loops which overlap on the conveyor belt present a much higher overall density of material on the sides than at the center. During the drying, thermosetting or expressing operation, the latter being effected by rubberized rolls in opposition, the effect of treatment is very different between the sides and the center of the band of yarn loops deposited on the conveyor.
At the moment of retraction of the yarn or synthetic thread, the geometry of the deposition in the form of round loops does not permit uniform retraction because of friction acting differently on the superposed yarn portions depending on whether these yarn portions form with each other very narrow or very wide angles. The consequences may be particularly inconvenient for certain realizations especially for the fabrication of yarns for tufted carpets cut at very small height which are piece-dyed after tufting.
These findings speak in favor of abandoning the deposition of round loops and the adoption of oval or flat loops.